The present invention relates to a physical value detecting apparatus using a housing in which a semiconductor device is housed, and a housing in which a semiconductor sensor device is housed for converting pressure and acceleration into electric signals and outputting the electric signals.
A semiconductor pressure sensor chip having a piezo resistance effect is generally used in a pressure detecting apparatus for measuring an engine intake pressure of an automobile. The principle of the semiconductor pressure sensor is well known. The semiconductor pressure sensor is constructed such that a bridge circuit of a plurality of semiconductor distortion gauges is formed on a diaphragm made of a material having a piezo resistance effect (such as single-crystal silicon). An electric signal is obtained from a change in gauge resistance of the semiconductor distortion gauges of the bridge circuit according to deformation of the diaphragm.
FIG. 10 is a view showing such a pressure detecting apparatus, and FIG. 11 is a sectional view taken along line 11-11 in FIG. 10. A pressure detecting apparatus 100 is constructed such that a sensor device 1 comprised of a base 11 made of glass, silicon, or the like, and a semiconductor pressure sensor chip 12 provided with a diaphragm 13 mounted on the base 11 is mounted in a concave portion 3 of a resin housing 2 formed of an injection molded thermosetting resin such as epoxy resin or a thermoplastic resin such as PPS (polyphenylene sulfide). Conventionally, an adhesive is disposed in the concave portion 3 of the resin housing 2, and the base 11 of the sensor device 1 is die-bonded with the adhesive. Then, lead terminals (lead frames) 5 for lead-out passing through the resin housing 2 and integrated with the resin housing 2 with an insertion molding are electrically connected to the semiconductor pressure sensor chip 12 with bonding wires 6.
The semiconductor pressure sensor chip 12 is joined to the base 11 so as to reduce stress applied from the resin housing 2. Further, a gel protective member 7 is used as a protective member for protecting a surface of the semiconductor pressure sensor chip 12 and the bonding wires 6 from contaminants included in a medium whose pressure is measured and for transmitting measured pressure to the semiconductor pressure sensor chip 12.
Further, a resin cap 8 formed of a material same as that of the resin housing 2 with the injection molding and having a pressure lead-in pipe 81 connected to a space to be measured is attached to the resin housing 2 to form a pressure detecting chamber 9. Pressure of the medium to be measured guided through the pressure lead-in pipe 81 is led into the pressure detecting chamber 9, and a change in the pressure in the pressure detecting chamber 9 is detected as a signal output from the sensor device 1 (refer to Japanese Patent Publication (Kokai) No. 2002-310836).
FIGS. 12 to 15 are enlarged views showing the concave portion 3 formed in the resin housing 2 in which the sensor device 1 of the pressure detecting apparatus 100 shown in FIG. 10 is housed. FIG. 12 is a plan view thereof, FIG. 13(a) is a sectional view taken along line 13(a)—13(a) in FIG. 12, and FIG. 13(b) is a sectional view taken along line 13(b)—13(b) in FIG. 12. For the sake of explanation, the bonding wires 6 are shown in FIG. 12 and FIG. 13(a). FIG. 14 is an enlarged view of a circled area in FIG. 13(b).
In the pressure detecting apparatus 100 described above, the concave portion 3 is formed to have an opening with an optimum dimension relative to the sensor device 1 so that the sensor device 1 can operate accurately and reliably, and also be made small. When the opening of the concave portion 3 is too small, the resin housing 2 may be deformed due to external stress from the resin cap 81 or thermal stress caused by an environmental temperature, thereby affecting and changing characteristics of the sensor device 1.
In particular, when positioning parts 31 protruding from the resin housing 2 at locations corresponding to corner parts 14 of the sensor device 1 are provided for preventing the sensor device 1 from being displaced in a direction θ, the corner parts 14 are located close to the positioning parts 31 and may contact with the positioning parts 31. Further, the positioning parts 31 and the corner parts 14 shown in FIGS. 12 and 13 make it difficult to insert the sensor device 1 into the concave portion 3 when the sensor device 1 is adhered to the concave portion 3.
Further, if a large amount of adhesive 4 is used for adhering the sensor device 1 to the resin housing 2, the adhesive 4 overflowing from a bottom of the sensor device 1 enters a space between the sensor device 1 and the base 11, so that a climbing part 41 is formed in the space between the sensor device 1 and the base 11. In this case, the deformation of the resin housing 2 is likely to affect and change the characteristics of the sensor device.
FIG. 15 is a sectional view similar to FIG. 13(b). As shown in FIG. 15, the bottom of the concave portion 3 of the resin housing 2 may have a saucer-shape with the injection molding due to a surface sink 42. When the bottom has such a variation in height, the resin housing 2 may contact the bottom of the sensor device at the corner parts 14, so that the deformation of the resin housing 2 affects and changes the characteristics of the sensor device. When the variation becomes greater than 10 μm, this problem is especially prominent. The problems described above are common in an apparatus such as an acceleration detecting apparatus as well as the pressure detecting apparatus, in which a physical value is converted into an electric signal.
In view of the problems described above, an object of the present invention is to provide a physical value detecting apparatus, in which a physical value is converted into an electric signal to be output. The physical value detecting apparatus is less susceptible to external stress or stress caused by deformation of a housing.
Further objects and advantages of the invention will be apparent from the following description of the invention.